An accountant with no medical training, Stocker Started treating wild animals in his garden shed in Aylesbury, Buckinghamshire, more than 20 years ago.
In 1991, Stocker was honoured by the Queen when she awarded him an MBE for his services to wildlife.
The funding that Stocker has received has been expertly managed' so that this unique hospital is self-supporting and every animal is treated free of charge.
Last year, Stocker, his wife Sue and son Colin opened a visitors' centre, incorporating an educational walk for adults and children.
Raising awareness of wildlife issues is an important part of the Stocker's work, and he has already noticed a shift in public perceptions.
More importantly, Stocker continues, ideas are changing about the need to save wildlife.
"Every animal that comes here is a trauma patient," explains Stocker. As a result of their injuries they are already in shock and by definition they are not used to the presence of humans.
"If we don't lose them overnight, we're surprised if we lose them at all," says Sue Stocker. During that time, the animal is stabilised and its injuries assessed.
When it came to releasing them, Stocker braved the elements to chaperone them back to their native colony.
It could not be released until it was able to feed itself, so Stocker spent painstaking hours training the toad to pick up food with its mouth.
Stocker has learned by a process of trial and error and is determined to disseminate the information that he has gathered as widely as possible.